The present invention describes a process for preparing glyoxylic acid by electrochemical reduction of oxalic acid in aqueous solution in divided or undivided electrolytic cells, wherein the cathode comprises carbon or at least 50% by weight of at least one of the metals Cu, Ti, Zr, V, Nb, Ta, Fe, Co, Ni, Zn, Al, Sn and Cr and the aqueous electrolysis solution in the undivided cells or in the cathode compartment of the divided cells in addition contains at least one salt of metals having a hydrogen overpotential of at least 0.25 V, based on a current density of 2500 A/m.sup.2. The process according to the invention has the advantage that inexpensive materials available on an industrial scale, in particular stainless chromium-nickel steels or graphite can be employed as the cathode material.